I am answering two questions, based on your inquiry. One can you sue a Virginia resident for a cause of action of alienation of affection (a north carolina law), not sure about virginia’s laws, that occurred in Virginia? Tkhe North Carolina court would need both subject matter jurisdiction and personal jurisdiction over the defendant, here the third party in Virginia. From the limited facts you stated, I do not think a court would have personal jurisdiction over that third party.
I do not have enough facts to say either way, but the statute on Personal Jurisdiction follows this reply. Remember, this is only intended as education and should not be acted upon without the advise of an attorney that is operating under all the relevant facts.
The second question: Are these facts relevant to prove or evidence of adultry? Yes. Regardless of where the actions evidencing adultry occurred, they are relevant.
Note: For statutes go to www.findlaw.com, states, NC